1. Field of the Invention
The present invention relates to hydrokinetic coupling apparatus, especially for a motor vehicle.
More particularly, the invention relates to a hydrokinetic coupling apparatus of the type comprising a casing having a generally transversely oriented wall adapted to be coupled in rotation to a driving shaft, a turbine wheel including an internal plate element and coupled in rotation to a hub which is adapted to be coupled in rotation to a driven shaft, a lock-up clutch interposed between the turbine wheel and the transverse wall, and comprising, in particular, arranged axially between the turbine wheel and the transverse wall, a generally transversely oriented piston, the radially inner portion of which is mounted for sliding movement along a cylindrical outer surface of a central sleeve, which is referred to as a guide sleeve for the piston, and an annular, transverse rear end face of which lies facing a front transverse face of the assembly consisting of the turbine wheel and hub.
2. Description of Related Art
One example of a hydrokinetic coupling apparatus of this kind is described and shown in the document FR-A-2 634 849 or U.S. Pat. No. 4,926,988.
In this type of design it is firstly necessary to provide an abutment for limiting the axial displacements of the piston towards the turbine wheel, and secondly to provide an abutment element acting as a spacer, which is interposed between the central sleeve and the hub of the turbine wheel, so as to determine a precise axial position between these two elements, and also in order to reduce to a minimum friction effects between these two elements, one of which rotates with respect to the other.
In the design according to the state of the art as constituted by the documents cited above, the piston abutment consists of an annular ring which is fitted in a groove formed in the central sleeve, while the spacer abutment between the central sleeve and the turbine wheel hub is an additional component which is made for example in the form of a washer.
This design is accordingly complex, in that it includes two components and necessitates, for the abutment for the piston, an additional machining operation in the central sleeve.
In order to overcome these drawbacks, the document FR-A-2 782 362 proposed thrust bearing means which are interposed axially between the annular transverse rear end face of the central sleeve and the said front transverse face of the assembly consisting of the turbine wheel and hub, whereby to limit friction between the said two elements that are rotatable with respect to each other, a portion of the thrust bearing being disposed facing a rear transverse face of the radially inner portion of the piston, so as to constitute an axial abutment defining the maximum rearward position of the piston when the clutch is disengaged.
In the design proposed in that document, the abutment means are made in the form of a single one-piece component which is interposed axially between the central sleeve and the hub of the turbine wheel, and the radial size of this component is such that it performs both of the abutment functions mentioned above at the same time.
This single abutment component is preferably made in a material having optimum friction characteristics so as to reduce friction between the rotating parts.
However, this design is not entirely satisfactory since the abutment is not positioned, especially in the radial direction. In addition, the compromise in the selection of a material having good enough ability to reduce friction, while being strong enough not to wear rapidly, is hard to optimise.
In order to provide a remedy for this disadvantage, the invention proposes a hydrokinetic coupling apparatus of the type mentioned above, characterised in that radial centring means are provided for centring the axial abutment with respect to the hub or with respect to the piston or with respect to the plate element.
Thanks to the invention, the axial abutment is centred in the radial direction. Preferably, the abutment means consist of an axial bearing with rolling elements, which is interposed axially between the annular transverse rear end face of the central sleeve and the said transverse front face of the assembly consisting of the turbine wheel and hub, and in that [sic] at least one ring of the axial thrust bearing includes a radially oriented annular portion which lies facing the said transverse rear face of the radially inner portion of the piston.
Because of this design, abutment means are provided which have reduced friction and high reliability, the design of which, since it makes use of one or two rings between which the rolling elements are arranged, offers numerous possibilities for the arrangement of this axial thrust bearing with rolling elements between the various components.
The axial thrust bearing is preferably a needle bearing.
According to further features of the invention:
the axial thrust bearing has at least one front ring interposed axially between the central sleeve and the rolling elements, and extending in a generally radial direction and in facing relationship with the said annular transverse rear end face of the central sleeve, the said front ring having an annular extension extending radially outwards beyond the ring and having a transverse front face in facing relationship with the said transverse rear face of the radially inner portion of the piston;
the hub includes a radially oriented plate portion extending outwards, and in that [sic] the said axial thrust bearing is disposed facing the transverse front face of the said plate portion;
the turbine wheel includes a generally radially oriented inner plate element or is connected to such a plate element, which is fixed to the plate portion of the hub;
the plate element of the turbine wheel is adjacent to the transverse front face of the plate portion of the hub;
the plate element of the turbine wheel is interposed axially between the plate portion of the hub and the axial thrust bearing;
the axial thrust bearing includes a rear ring interposed axially between the assembly consisting of the turbine wheel and hub;
the rear ring of the axial thrust bearing is centred radially with respect to the plate portion of the hub, or with respect to the said plate element of the turbine wheel;
the rear ring of the axial thrust bearing is centred radially outwardly with respect to the inner periphery of the said plate element;
the rear ring of the axial thrust bearing is centred radially inwardly with respect to the plate portion of the hub;
the front ring of the axial thrust bearing is centred radially with respect to the central sleeve;
the front ring of the axial thrust bearing is centred radially with respect to the radially inner portion of the piston;
one ring of the axial thrust bearing is coupled in rotation to the turbine wheel, or to the central sleeve, or to the piston;
the axial thrust bearing is attached axially to the turbine wheel, or to the central sleeve, or to the piston.